41-year-old male with stage IV rectal adenocarcinoma (cT4bN2M1a) with pulmonary metastases, chronic kidney disease stage II (eGFR ≈ 66 mL/min/1.73 m²), anemia of chronic disease, gout on febuxostat, presenting with a ruptured left perianal soft‑tissue abscess, fever, hypotension (BP 88/63 mmHg), tachycardia (HR 112 bpm), leukocytosis and elevated procalcitonin indicating sepsis—what is the diagnosis and appropriate management?

Diagnosis and Management of Septic Perianal Abscess in an Immunocompromised Cancer Patient

This patient requires immediate surgical drainage with broad-spectrum antibiotics covering MRSA and anaerobes, aggressive resuscitation, and urgent surgical consultation for wound exploration and debridement given his septic presentation with hypotension, tachycardia, and elevated procalcitonin in the setting of recent chemotherapy and stage IV rectal adenocarcinoma. 1

Diagnosis

Primary Diagnosis: Sepsis Secondary to Complicated Perianal Abscess

The clinical presentation confirms sepsis from a complicated soft tissue infection based on:

• Hemodynamic instability with hypotension (BP 88/63 mmHg) and tachycardia (HR 112 bpm) meeting septic shock criteria (MAP <65 mmHg) 2
• Marked leukocytosis (WBC 20.8 × 10⁹/L with 88% neutrophils) and elevated procalcitonin (0.61 ng/mL) indicating bacterial sepsis 1
• Ruptured 3×3 cm perianal abscess with blood-mixed purulent discharge, surrounding erythema and swelling 1
• High-risk host factors: recent chemotherapy (5 days post-cycle), stage IV malignancy with metastases, anemia (Hgb 88 g/L), CKD stage II, and thrombocytosis (682 × 10⁹/L) suggesting systemic inflammation 1, 3

Classification and Risk Stratification

This represents a complicated SSTI (Class 3-4 by Eron classification) with systemic toxicity requiring hospitalization and aggressive intervention 1. The patient demonstrates:

• Class 3 features: toxic appearance with fever, tachycardia, and hypotension 1
• Complicated SSTI criteria: deep soft-tissue involvement requiring significant surgical intervention beyond simple drainage 1
• High risk for drug-resistant organisms: immunocompromised state from chemotherapy, recent hospitalization, and perianal location with fecal contamination 3

Critical Exclusion: Necrotizing Fasciitis (Fournier's Gangrene)

Immediate evaluation for necrotizing soft tissue infection is mandatory given the high mortality (up to 88% if delayed) 4. Warning signs to assess:

• Rapidly spreading erythema beyond the abscess margins 4
• Crepitus or skin necrosis on examination 4
• Pain disproportionate to physical findings (hallmark of necrotizing fasciitis) 4
• Skin changes: dusky discoloration, bullae, or areas of anesthesia 4

The current presentation shows localized erythema and swelling without these features, but serial examinations every 4-6 hours are essential as necrotizing infections can evolve rapidly in immunocompromised patients 4.

Immediate Management

1. Resuscitation and Hemodynamic Support

Aggressive fluid resuscitation with crystalloids is the first priority to restore tissue perfusion 1:

• Initial bolus: 30 mL/kg (approximately 1,600 mL for this 54 kg patient) within the first 3 hours 1
• Target MAP ≥65 mmHg with fluid resuscitation before initiating vasopressors 1, 2
• If hypotension persists after adequate fluid resuscitation, initiate norepinephrine as first-line vasopressor 1
• Monitor lactate clearance and urine output as markers of adequate resuscitation 1

The current plan of PNSS 80 cc/hr is inadequate for septic shock resuscitation and must be increased immediately 1.

2. Antibiotic Therapy

The current empiric regimen of piperacillin-tazobactam 4.5g IV q6h plus metronidazole 500mg IV q8h is appropriate for complicated perianal abscess with sepsis 1, 3. Key considerations:

Empiric Coverage Rationale

• Piperacillin-tazobactam provides broad-spectrum coverage against Enterobacteriaceae, Pseudomonas, and anaerobes commonly found in perianal abscesses 1, 3
• Metronidazole addition ensures optimal anaerobic coverage (Bacteroides species) which is critical in perianal infections 1
• MRSA coverage consideration: Given immunocompromised status and recent chemotherapy, consider adding vancomycin 15-20 mg/kg IV q8-12h (adjusted for CKD stage II with eGFR 66) if clinical deterioration occurs or MRSA risk factors present 1, 3

Culture-Directed Therapy

• Obtain cultures of purulent drainage during surgical exploration to guide antibiotic de-escalation 1, 3
• Blood cultures should be obtained immediately given septic presentation 1
• High rates of drug-resistant organisms (including ESBL-producing E. coli and resistant Staphylococcus species) are documented in perianal abscesses, particularly in immunocompromised patients 3

Duration of Therapy

• Continue IV antibiotics until clinical improvement: resolution of fever, normalization of WBC, hemodynamic stability, and ability to tolerate oral intake 1
• In immunocompromised patients with drained abscess and surrounding cellulitis, antibiotic therapy is strongly recommended beyond simple drainage 1
• Typical duration: 7-14 days depending on clinical response and extent of soft tissue involvement 1

3. Urgent Surgical Source Control

Surgical incision and drainage is mandatory and should not be delayed 1. The surgical plan is appropriate but requires clarification:

Timing of Surgery

• Emergency surgery is indicated given septic shock presentation 1
• "Once stable" is inappropriate phrasing—surgery should proceed within 6-12 hours after initial resuscitation begins, not delayed until complete hemodynamic normalization 1
• Every hour of delay increases mortality risk in septic patients requiring source control 1

Surgical Approach

• Wound exploration under anesthesia (EUA) with adequate debridement of all necrotic tissue and loculations 1
• Assess for underlying fistula: In this patient with rectal adenocarcinoma and prior loop ileostomy, do not probe for fistula during acute drainage to avoid iatrogenic complications 1
• If obvious fistula involving sphincter muscle is identified, place a loose draining seton rather than performing fistulotomy 1
• Adequate drainage with dependent positioning of the wound 1

Wound Management Post-Drainage

• Daily wound care with normal saline irrigation and gauze packing is appropriate 1
• No definitive recommendation exists regarding packing versus non-packing after drainage, but packing helps maintain drainage in deep cavities 1
• Serial examinations to monitor for: spreading infection, wound healing, and need for re-debridement 4, 3

4. Monitoring and Reassessment

Close monitoring for treatment failure and complications is essential in this high-risk patient 4, 3:

Laboratory Monitoring

• Daily CBC, inflammatory markers (CRP, procalcitonin), serum creatinine, and electrolytes to assess response to therapy 1
• Procalcitonin is particularly useful for monitoring antibiotic response and can guide duration of therapy 1
• Lactate clearance as a marker of adequate resuscitation 1

Clinical Red Flags Requiring Immediate Re-evaluation

• Spreading erythema, skin discoloration, or blistering suggesting necrotizing infection 4
• Persistent fever or hemodynamic instability after 48-72 hours of appropriate therapy 1, 3
• Worsening pain or new areas of fluctuance indicating inadequate drainage or new abscess formation 4
• Need for re-debridement: Higher rates documented in patients with drug-resistant organisms 3

Imaging Considerations

• CT pelvis with IV contrast or MRI if clinical deterioration occurs, to evaluate for: 1
  • Deeper extension (supralevator or ischiorectal spaces)
  • Undrained fluid collections
  • Necrotizing fasciitis
  • Tumor-related complications (perforation, fistula)

Special Considerations in This Patient

1. Oncologic Context

The underlying stage IV rectal adenocarcinoma significantly impacts management 1:

• Tumor-related fistula or perforation must be considered in differential diagnosis 1
• Coordination with oncology regarding chemotherapy delay until infection resolves 1
• Prognosis discussions given advanced malignancy and serious infection complication

2. Renal Function and Medication Adjustments

CKD stage II (eGFR 66 mL/min/1.73 m²) requires dose adjustments 1:

• Piperacillin-tazobactam: Reduce to 3.375g IV q6h for eGFR 40-80 mL/min
• Metronidazole: No adjustment needed
• Febuxostat: Continue current dose (40mg daily)—demonstrated renal safety in stage 4-5 CKD 5, 6
• Monitor renal function closely as sepsis can precipitate acute kidney injury 1

3. Anemia Management

Severe anemia (Hgb 88 g/L) in septic patient requires assessment 1:

• Transfusion threshold: Consider transfusion if Hgb <70 g/L or if hemodynamically unstable with ongoing bleeding 1
• Continue iron supplementation once acute infection controlled
• Investigate for ongoing bleeding from tumor or surgical site

4. Immunocompromised Status

Recent chemotherapy (5 days post-cycle) creates highest risk period for severe infection 1, 3:

• Neutropenic fever protocols may apply if absolute neutrophil count drops below 1.0 × 10⁹/L
• Lower threshold for ICU admission and aggressive intervention 1
• Consider G-CSF if neutropenia develops, in consultation with oncology

Disposition and Follow-Up

ICU admission is appropriate given septic shock presentation requiring close hemodynamic monitoring and potential vasopressor support 1.

Surgical follow-up within 48-72 hours post-drainage to assess wound healing and plan definitive fistula management if indicated (delayed until infection resolved and patient stable) 1.

Oncology consultation to discuss chemotherapy timing—typically delayed 2-4 weeks after resolution of serious infection 1.